Javascript no longer works

Some browsers updated their security policies and your issue might be due to stricter security policies that were implemented to prevent this kind of direct interaction between windows that are opened from different origins.

To ensure cross-browser compatibility, I would use the 'window.postMessage()' method as this method exchange messages between windows, even across different origins.

In the parent page, I will add the following to use window.postMessage() -

//handle messages from the child page
function receiveMessageFromChild(event) {
  if (event.origin !== window.location.origin) {
    // Reject messages from unknown origins for security
    return;
  }

  // actions when message is received from the child page
  // for example, reload the parent page
  if (event.data === "reloadParent") {
    window.location.reload(true);
  }
}

// receive messages from the child page
window.addEventListener("message", receiveMessageFromChild, false);

// function to open the child page
function openChildPage() {
  // open the child page
  var childPage = window.open("child.html");

  // actions after opening the child page
  // for example, send a message to the child page
  childPage.postMessage("activateParent", window.location.origin);
}

and in the child page -

// handle messages received from the parent page
function receiveMessageFromParent(event) {
  if (event.origin !== window.location.origin) {
    // reject messages from unknown origins for security
    return;
  }

  // actions when message is received from the parent page
  // for example, notify the parent to reload
  if (event.data === "activateParent") {
    window.opener.postMessage("reloadParent", window.location.origin);
  }
}
// receive messages from the parent page
window.addEventListener("message", receiveMessageFromParent, false);

You can read more on this method at Window: postMessage() method[^]